c++ - Retrieve value of QTableWidget cells which are QLineEdit widgets -

i create qlineedit,set validator , put on table code:

ui->moneytablewidget->setcellwidget(rowsnum, 1, newqlineedit); 

then i've got another class manipulating table's data doing sum of every value of column. here's code:

int calculator::calculatepricessum(qtablewidget &moneytablewidget){     double total = 0;     qwidget *tmplineedit;     qstring *tmpstring;     for(int row=0; row<moneytablewidget.rowcount(); row++){         tmplineedit = (qlineedit*)moneytablewidget.cellwidget(row,1);                tmpstring = tmplineedit.text();         total += tmpstring->todouble();     }     return total; } 

but building fails error:

/home/testpec/src/nokia qt/moneytracker-build-simulator/../moneytracker/calculator.cpp:11: error: cannot convert ‘qlineedit*’ ‘qwidget*’ in assignment

why convertion error?

another subquestion: passing table reference saves memory right? problem? im developing nokia smartphone , think passing object value waste of memory...(sorry if dumb question i'm little rusty c++ , pointers stuff...)

when declare tmplineedit, should declaring qlineedit* instead of qwidget*. loop grabs widget, casts qlineedit* , tries put qwidget*. also, i'd recommend using qobject_cast<qlineedit*> (or dynamic_cast) can ensure cast succeeded.

int calculator::calculatepricessum(qtablewidget &moneytablewidget){     double total = 0;     qlineedit* tmplineedit;     qstring tmpstring;     for(int row=0; row < moneytablewidget.rowcount(); row++)     {         tmplineedit = qobject_cast<qlineedit*>(moneytablewidget.cellwidget(row,1));         if(null == tmplineedit)         {             // indicate failure.         }         tmpstring = tmplineedit->text();         total += tmpstring.todouble();     }     return total; } 

as second question, passing reference idea - know of classes in qt (qimage in particular) use reference counting , implicit sharing can pass around value without worrying implications of large copy operations, i'm not sure if qtablewidget in category well.